1. Field of the Invention
The present invention relates to an optical apparatus having a movable optical unit for use as an optical means that optically compensates an image blur.
2. Related Background Art
An optical apparatus with an optical unit that is movable in a light beam deflecting direction has been applied to an apparatus that optically prevents an image blur.
Next, an image blur prevention apparatus will be described.
In modern cameras, all important operations such as an exposing operation and focusing operation are automatically performed. Thus, even if the user of such a camera is not familiar with its operations, chances of mistakes of photographing are very low. However, so far automatic prevention of mistakes of photographing due to vibration has been difficult.
In recent years, cameras that can prevent mistakes of photographing due to vibration have been intensively studied. In particular, cameras that can prevent mistakes of photographing due to vibration caused by the user have been developed and studied.
The frequencies of vibration of cameras are normally in the range from 1 Hz to 12 Hz. When the shutter of the camera is released, vibration takes place. To correctly photograph images without an image blur regardless of whether or not vibration takes place, the vibration of the camera should be detected and an auxiliary lens should be displaced corresponding to a detected value. Thus, to photograph images free from an image blur, first the vibration of the camera should be accurately detected. Second, the displacement of optical axis due to the vibration should be compensated.
The vibration (of a camera) can be theoretically detected with a vibration sensor that detects angular acceleration, angular velocity, angular displacement, or the like and a camera vibration detection means that electrically or mechanically integrates an output signal of the vibration sensor and outputs information as the angular displacement. The detected information is sent to a correction optical means. The correction optical means deflects a photographic optical axis corresponding to the detected information.
Next, an image blur prevention system with such an angular displacement detection means will be described with reference to FIG. 37.
FIG. 37 shows a system that suppresses an image blur caused by a vertical vibration 41p and a horizontal vibration 41y that are applied to a camera. The vertical vibration 41p and the horizontal vibration 41y are denoted by arrows of FIG. 37.
In FIG. 37, reference numeral 42 is a lens barrel. Reference numeral 43p is an angular displacement detection means for detecting an angular displacement of the camera's vertical vibration 44p. Reference numeral 43y is an angular displacement detection means for detecting an angular displacement of the camera's horizontal vibration 44y. Reference numeral 45 is a correction optical means. (Reference numerals 46p and 46y are coils that supply thrusting force to the correction optical means 45. Reference numerals 47p and 47y are position detection devices that detect a position of the correction optical means 45). The correction optical means 45 has a position control loop (that will be described later). The correction optical means 45 is driven corresponding to outputs of the angular displacement detection means 43p and 43y so as to stabilize an image plane 48.
FIG. 38 is an exploded perspective view showing a construction of the aforementioned correction optical means.
A lens 71 is caulked in a support frame 72. A bearing 73y is fitted to the support frame 72 under pressure. A support shaft 74y is supported by the bearing 73y so that the support shaft 74y is axially slidable. A cavity portion 74ya of the support shaft 74y is hooked by a nail 75 of the support arm 75. A bearing 73p is fitted to the support arm 75 under pressure. The support shaft 74p is supported so that it is axially slidable.
FIG. 38 also shows a rear view of the support arm 75 and a partial front view of the nail 75a.
The support frame 72 has holes 72pa and 72ya for light emitting devices 76p and 76y such as IREDs or the like. Terminals of the light emitting devices 76p and 76y are soldered to lids 77p and 77y that serve as adhering boards, respectively. (The lids 77p and 77y are adhered to the support frame 72.) The support frame 72 has slits 72pb and 72yb. Rays of light emitted from the light emitting devices 76p and 76y are transmitted to PSDs 78p and 78y (that will be described later) through the slits 72pb and 72yb, respectively. Coils 79p and 79y are adhered to the support frame 72. Terminals of the coils 79p and 79y are soldered to the lids 77p and 77y, respectively.
A support ball 711 is fitted in the lens barrel 710 (at three positions). The cavity portion 74pa of the support shaft 74p has a hooking nail portion 710a.
Yokes 712p1, 712p2, 712p3, and a magnet 713p are layered and adhered to each other. Likewise, yokes 712y1, 712y2, 712y3, and a magnet 713y are layered and adhered to each other. Polarities of the magnets 713p and 713y are denoted by arrows of the drawing.
The yokes 712p2 and 712y2 are secured to cavity portions 710pb and 710b of the lens barrel 710 with screws, respectively.
The position detection devices 78p and 78y made of for example a PSD are adhered to sensor bases 714p and 714y (reference numeral 714y not shown), respectively. Terminals of the position detection devices 78p and 78y are soldered to a flexible board 716 through sensor masks 715p and 715y, respectively. Protrusion portions 714pa and 714ya (reference numeral 714ya not shown) of the sensor bases 714p and 714y are inserted into holes 710pc and 710yc of the lens barrel 710, respectively. The flexible board 716 is secured to the lens barrel 710 through a flexible stay 717 with a screw. Edge portions 716pa and 716ya of the flexible board 716 are secured to the yokes 712p1 and 712y1 through holes 710pd and 710yd of the lens barrel 710, respectively. The terminals for the coil and the light emitting device on the lids 77p and 77y are connected to round portions 716pb and 716yb of the edge portions 716p and 716ya on the flexible board 716 with a polyurethane coated copper cable (three-wire stranded cable).
A plunger 719 is secured to a mechanical lock chassis 718 with a screw. The plunger 719 is fitted to a mechanical lock arm 721 charged with a spring 720. The plunger 719 is rotatably secured to the mechanical lock chassis 718 with a shaft machine screw 722.
The mechanical lock chassis 718 is secured to the lens barrel 710 with a screw. Terminals of the plunger 719 are soldered to the round portion 716b of the flexible board 716.
An adjusting screw 723 has a spherical head. The adjusting screw 723 is secured to a yoke 712p and the mechanical lock chassis 718 (at three positions). A sliding surface (hatched portion 72c) of the support frame 72 is surrounded by the adjusting screw 723 and the support ball 711. The adjusting screw 723 is secured so that it is opposed to the sliding surface with a small clearance.
A cover 724 is adhered to the lens barrel 710 so as to cover the correction optical means.
FIGS. 39A and 39B are schematic diagrams for explaining a drive control operation of the correction optical means shown in FIG. 38.
The outputs of the position detection devices 78p and 78y are amplified by amplifying circuits 727p and 727y, respectively. The outputs of the amplifiers 727p and 727y are sent to the coils 79p and 79y. Thus, the support frame 72 is driven and thereby the outputs of the position detection devices 78p and 78y vary. When the coils 79p and 79y are driven in the directions that the outputs of the position detection devices 78p and 78y decrease (namely, negative-feedback is performed), the support frame 72 is stably placed at a position where the outputs of the position detection devices 78p and 78y become almost zero. Addition circuits 731p and 731y add outputs of the position detection devices 78p and 78y and command signals 730p and 730y that are received from the outside of the apparatus, respectively. Compensation circuits 728 and 728y stabilize a control system. Drive circuits 729p and 729y compensate currents that flow in the coils 79p and 79y.
When the command signals 730p and 730y are sent to the system shown in FIGS. 39A and 39B through the addition circuits 731p and 731y, respectively, the support frame 72 is accurately driven according to the command signals 730p and 730y.
The technique for controlling a coil with a negative feedback of a position detection output as in the system shown in FIGS. 39A and 39B is referred to as position control technique. When the amount of vibration is given as the command signals 730p and 730y, the support frame 72 is driven corresponding to the amount of vibration.
FIG. 40 is a circuit diagram showing the drive control system of the correction optical means shown in FIGS. 39A and 39B. With reference to this drawing, the drive control system for a pitch direction 725p will be described (this is because the drive control system for a yaw direction 725y is similar to that for the pitch direction 725p).
The light emitting device 76p causes optical currents 727i1 and 727i2 to flow in the position detection device 78p (constructed of resistors R1 and R2). Current-voltage conversion amplifiers 727a and 727b convert the optical currents 727i1 and 727i2 into voltages, respectively. A differential amplifier 727c obtains the difference between the outputs of the current-voltage conversion amplifiers 727a and 727b (namely, the output proportional to the position of the support frame 72 in the.pitch direction 725p). The amplifier 727p shown in FIGS. 39A and 39B is constructed of the current-voltage conversion amplifiers 727a and 727b, the differential amplifier 727c, and resistors R3 to R10.
A command amplifier 731a adds the command signal 730p, which is received from the outside of the system, and a differential signal of the differential amplifier 727c. The addition circuit 731p shown in FIGS. 39A and 39B is constructed of the command amplifier 731a and resisters R11 to R14.
Resistors R15 and R16 and a condenser C1 construct a known phase advancing circuit. The phase advancing circuit is equivalent to a compensation circuit 728p shown in FIGS. 39A and 39B.
An output of the addition circuit 731p is sent to a drive amplifier 729a through the compensation circuit 728p. The drive amplifier 729a generates a drive signal of the pitch coil 79p. With the drive signal, the correction optical means is displaced. The drive amplifier 729a, a resistor R17, and transistors TR1 and TR2 construct the drive circuit 729p shown in FIGS. 39A and 39B.
An addition amplifier 732a adds the outputs of the current-voltage conversion amplifiers 727a and 727b (namely, total amount of light received by the position detection device 78p). The output of the addition amplifier 732a is sent to a drive amplifier 732b. Thus, the drive amplifier 732b drives the light emitting device 76p corresponding to the output signal of the addition amplifier 732a. The addition amplifier 732a, the drive amplifier 732b, resistors R18 to R22, and a condenser C2 construct a drive circuit (not shown in FIGS. 39A and 39B) of the light emitting device 76p.
The amount of light emitted by the emitting device 76p unstably varies depending on changes of temperature. Thus, the position detection sensibility of the differential amplifier 727c accordingly varies. However, when the drive circuit controls the light emitting device 76p so that the total amount of light received becomes constant, the fluctuation of the position detection sensitivity can be reduced.
As described above, when the correction optical means shown in FIGS. 38 to 39B is driven, if no command is received from the vibration detection means, the support frame 72 is stably placed at a position where the position detection output of the position detection means (constructed of the light emitting devices 76p and 76y, the slits 72pb and 72yb, and the position detection devices 78p and 78y) becomes almost zero. In other words, when the pitch direction 725p (shown in FIGS. 39A and 39B) is the direction of gravity, the support frame 72 is always gravitated. Thus, to stabilize the support frame 72, a drive current flows in the coil 79p so as to support the support frame 72 against gravity.
To do that, coil springs 61pa, 61pb, 61ya, and 6lyb are disposed between the lens barrel 710 (nail portion 710a) and the support frame 72 so that the support frame 72 and the lens barrel 710 are surrounded by such elastic members.
In FIG. 41, the coil springs 61pa and 61pb have the same spring constant and are disposed around the support shaft 74p. One end of each of these coil springs 61pa and 61pb is in contact with the nail portion 710a. The other end of the coil spring 61pa is in contact with an inner surface 75b of a rear flange portion of the support arm 75, whereas the other end of the coil spring 61pb is in contact with an inner surface 75c of a rear flange of the support arm 75. In such a manner, the coil springs 61pa and 61pb are pre-charged.
Likewise, the coil springs 61ya and 6lyb have the same spring constant and are disposed around the support shaft 74y. One end of each of the coil springs 61ya and 6lyb is in contact with the nail member 75a of the support arm 75. The other end of the coil spring 61ya is in contact with an opposed wall 72d of the support frame 72, whereas the other end of the coil spring 6lyb is in contact with an opposed wall 72e of the support frame 72.
Thus, the support frame is surrounded by the pre-charged springs with the same spring constant. When the length of the coil spring 61pa becomes the same as the length of the coil spring 61pb and when the length of the coil spring 61ya becomes the same as the length of the coil spring 6lyb, the support frame 72 is balanced. Thus, the support frame 72 can be supported by the spring force against the gravity. As a result, the amount of currents that flow in the coils 79p and 79y can be reduced.
However, the balanced positions of the support frame 72 by the springs do not always accord with the zero positions of the position detection devices 78p and 78y. This is because there are many error factors such as accuracies of the springs, part accuracies of the support frame 72, the support arm 75, and the lens barrel 710, the mounting accuracies of the position detection devices 78p and 78y against the lens barrel 710, the relative error of a detecting chip 78a against a package 78b of each position detection device, and so forth.
As shown in FIG. 41, if an error 6 takes place between a balance point 63 of the springs in a drive direction 65 of the support frame 72 against the gravity g in a direction denoted by an arrow 62 and a center 64 at which the output of the position detection device 78p becomes zero (this center 64 is referred to as output zero center), a current equivalent to force 2.delta.k should continuously flow in the coil 79p so as to keep the support frame 72 at the output zero center 64 (where k is the spring constant of the coil springs 61pa and 61pb).
The spring constant k of the coil springs 61pa and 61pb cannot be decreased. In other words, when the spring constant k is decreased, the balance point against the gravity g lowers. Thus, the relative distance between the nail portion 710a and the flange inner surface 75c shortened and thereby the drive stroke of the support frame 72 against vibration becomes small. Consequently, the apparatus cannot be prevented from large vibration. As a result, the force 2.delta.k cannot be reduced. In other words, the amount of coil current cannot be remarkably decreased in comparison with a construction that does not use coil springs.
As described above, in the conventional image blur prevention apparatus, currents that flow in coils are required so as to keep the apparatus against gravity or the force of coil springs. Thus, the conventional image blur prevention apparatus is not suitable for home-use appliances such as still cameras and video cameras that have limited batteries.
In the conventional construction shown in FIGS. 37 to 41, a securing means of the correction optical means is constructed of the mechanical lock chassis 718, the plunger 719, the mechanic arm 721, and so forth. The securing means is secured to the lens barrel 710 with a screw. While an image blur prevention function is not working, the securing means secures the support frame 72 so that it does not move in directions of arrows denoted by 725p and 726y as shown in FIGS. 39A and 39B. While the image blur prevention function is working, the image blur prevention lens system is designed so that its optical characteristics do not degrade even if the lens 71 moves in the directions of the arrows 725p and 726y. Thus, while the support frame 72 is secured, even if the optical axis of the lens 71 does not accord with the optical axis of the lens barrel, satisfactory optical characteristics can be obtained. Thus, so far it was not necessary to designate the secured positions of the lens 71 in the directions of the arrows 725p and 726y. In other words, the lens 71 could be secured at any position in the directions of the arrows 725p and 726y.
However, in the case that the secured position of the lens 71 largely deviates from the optical axis of the lens barrel, if the image blur prevention function is not used, the following problems take place.
In FIG. 42, when a user aims an image blur prevention camera at an object 61 (while the image blur prevention function is not working, the correction optical means is secured by the securing means), if a photographic optical axis is deviated by the correction optical means, the orientation of the image blur prevention camera 62 deviates from the photographic optical axis so as to improve a framing. Thus, the user can take a picture without a strange feeling.
In addition, as described above, while the image blur prevention function is working, the securing means is detached from the correction optical means. The correction optical means is stably placed at a position where the outputs of the position detection devices 78p and 78y become almost zero. The correction optical means is driven based on this position corresponding to the output of the vibration detection means. Thus, if the secured position of the correction optical means deviates from the output zero points of the position detection devices 78p and 78y, the following problem will take place.
In FIG. 43A, vertical axis represents positions of the correction optical means in the directions 725p and 726y. (In this drawing, the positions of the correction optical means in the direction 725p are shown.) While the image blur prevention function is working, the correction optical means is secured at a position represented by a solid line 51. A solid line 52 represents a position at which the outputs of the position detection devices 78p and 78y become zero. A one-dashed line represents the optical axis of the lens barrel.
When the user aims the camera at an object for a framing and turns on the image blur prevention function, the position of the correction optical means moves from the position 51 to the position 52. Thus, as shown in FIG. 43B, the object 54, namely framing, varies as shown by a dotted line 55.
To restore the original framing, the user should change the orientation of the image blur prevention lens. At this point, if the user changes the orientation (posture) of the camera as shown by the one-dashed line 57 of FIG. 44, the original framing is supposed to take place. However, since the image blur prevention function is working, even if the orientation of the image blur prevention lens is changed, the framing is not immediately changed. Thus, the user tends to excessively change the orientation of the camera. As a result, as shown by a solid line 58, the user cannot immediately aim the camera at the object.
Next, with reference to FIGS. 37 to 41, the operation of the image blur prevention function of the conventional correction optical means will be described time by time.
In FIG. 45A, reference numeral 743 is a position of the correction optical means when the support frame 72 is locked by the mechanical lock arm 721. Reference numeral 744 is a position of the correction optical means when the mechanical lock arm 721 is detached and a position control is performed for the lens 71. The position 744 is the center of an electric spring. When the image blur prevention function is turned on by an external switch operation (at point 745), the mechanical lock arm 721 is detached from the support frame 72. Thus, the lens 71 is moved from the position 743 to the position 744. When a release button is pressed by half, a switch SW1 is turned on (at point 747). At this point, as shown in FIG. 45C, a command signal 746 with a level of zero is input to the correction optical means. Thus, the correction optical means is driven according to the command signal 746. When the user releases the release button (at point 748), the correction optical means returns to the position 744. It should be noted that the image blur prevention function may be turned on by the switch SW1 and thereby the mechanical lock arm 721 may be detached from the support frame 72.
When the orientation of the camera is changed (749), the correction optical means moves to position 750. This is because the direction of the gravity g (751) varies and thereby the balance position of the weight of the lens 71, the gravity, and the electric spring force varies.
At this point, when the release button is pressed by half, the switch SW1 is turned on (point 752). Thus, the correction optical means is driven corresponding to a command signal 753 with a level of zero. When the user releases the release button (at point 754), the correction optical means returns to the position 750.
FIG. 45B shows power consumption of the coils 78p and 78y of the correction optical means. As shown by a hatched region, after the image blur prevention function is turned on, a large amount of constant power is required. (In contrast, the power consumption for image blur correction function in image blur prevention sections 755 and 756 is much smaller than the power consumption of the entire power consumption of the system.) Such a large amount of power is required for always keeping the correction optical means at the center of the electrical spring against the gravity g (751). When the direction of the gravity g varies as the orientation of the camera varies in a period 749, the power consumption slightly decreases. When the camera is oriented upward so as to prevent the correction optical means from being gravitated in the drive direction thereof, the power consumption for the gravity g is eliminated.
However, since the camera is likely to be used in its flat position, constant power is always required. However, since the battery of the camera only has a limited amount of power, the number of films that the camera can photograph is limited.
To prevent such a problem, a related art reference as disclosed in Japanese Patent Laid-Open Application No. 4-39616 is known. In the related art reference, a correction optical means is mechanically supported by a spring. In addition, a high-pass filter with a large time constant is connected in series with a position control loop. Thus, the correction optical means does not work for a DC component such as gravity.
In this case, as shown in FIG. 46A, when the image blur prevention function is turned on (at point 745), the correction optical means moves to the center position 744 of the electrical spring. However, due to the high-pass filter, the correction optical means gradually moves to a center position 757 of a mechanical spring. Thus, as shown in FIG. 46B, the power consumption gradually decreases to zero. Even if the posture of the camera varies (in period 749), the direction of the gravity g varies and thereby the center of mechanical spring moves to position 758. However, due to the high-pass filter, the correction optical means gradually moves to the center position of the mechanical spring. Only while the correction optical means is moving to the center position of the mechanical spring, power consumption takes place (763). However, power is not consumed for the gravity g. Thus, in comparison with the construction shown in FIG. 45B, power consumption can be much reduced. However, in this related art reference, there is the following problem.
After the image blur prevention function has been turned on (point 745), while the posture of the camera is changing (749) and thereby the correction optical means is moving to the center position of the mechanical spring 757, power consumption takes place (763). Thus, the quicker the correction optical means moves to the center position of the mechanical spring 757, the less power is consumed. However, in such a construction, the correction optical means gradually moves to the center position of the mechanical spring 757 while the image blur prevention function is working (745) and the posture of the camera is changing (749). Thus, it takes a relatively long time.
In addition, in the construction of the abovementiond related art reference, since the correction optical means is supported by springs, when the correction optical means is driven corresponding to the command signals 746 and 753 as shown in FIG. 46C, the correction optical means should be driven against the spring force. Thus, the power consumption in the image blur prevention sections 755 and 756 is large. Moreover, the amplitudes of the command signals become large time by time. The spring force that moves the correction optical means becomes large (due to large stroke). Thus, the power consumption becomes large. When the power consumption exceeds threshold values 764 and 765, the power supply to other functions of the camera is adversely affected.